Electric power steering apparatus

ABSTRACT

An electric power steering apparatus including: a steering angle control section that calculates a motor current command value and a switching section that inputs the motor current command value to switch. The steering angle control section has a feedback control section that generates a feedback control current command value; an SAT compensating section that generates an SAT compensation current command value; and an output section that generates the motor current command value from the feedback control current command value and the SAT compensation current command value. The switching section is switched depending on a switching command of an automatic steering mode and a manual steering mode, a motor is drive-controlled based on the motor current command value in the automatic steering mode.

TECHNICAL FIELD

The present invention relates to an electric power steering apparatusthat has functions of an automatic steering mode (parking support mode)and a manual steering mode and provides a steering system of a vehiclewith an assist force generated by a motor, and in particular to anelectric power steering apparatus capable of further improving afollow-up capability of an actual steering angle to a target steeringangle in the automatic steering mode.

BACKGROUND ART

An electric power steering apparatus which provides a steering mechanismof a vehicle with a steering assist torque (an assist torque) by meansof a rotational torque of a motor, applies a driving force of the motoras the steering assist torque to a steering shaft or a rack shaft bymeans of a transmission mechanism such as gears or a belt through areduction mechanism. In order to accurately generate the steering assisttorque, such a conventional electric power steering apparatus (EPS)performs a feedback control of a motor current. The feedback controladjusts a voltage supplied to the motor so that a difference between asteering assist command value (a current command value) and a detectedmotor current value becomes small, and the adjustment of the voltageapplied to the motor is generally performed by an adjustment of dutycommand values of a PWM (Pulse Width Modulation) control.

A general configuration of the conventional electric power steeringapparatus will be described with reference to FIG. 1. As shown in FIG.1, a column shaft (a steering shaft) 2 connected to a steering wheel 1,is connected to steered wheels 8L and 8R through reduction gears 3,universal joints 4 a and 4 b, a rack and pinion mechanism 5, and tierods 6 a and 6 b, further via hub units 7 a and 7 b. Further, the columnshaft 2 is provided with a torque sensor 10 for detecting a steeringtorque of the steering wheel 1, and a motor 20 for assisting thesteering force of the steering wheel 1 is connected to the column shaft2 through the reduction gears 3. Electric power is supplied to a controlunit (ECU) 100 for controlling the electric power steering apparatusfrom a battery 13, and an ignition key signal is inputted into thecontrol unit 100 through an ignition key 11. The control unit 100calculates a steering assist command value of an assist (steeringassist) command based on a steering torque Th detected by the torquesensor 10 and a vehicle velocity Vel detected by a vehicle velocitysensor 12, and controls a current supplied to the motor 20 based on acurrent control value E obtained by performing compensation and so onwith respect to the steering assist command value. Moreover, it is alsopossible to receive the vehicle velocity Vel from a CAN (Controller AreaNetwork) or the like.

In such an electric power steering apparatus, conventionally, forexample, as disclosed in Japanese Published Unexamined PatentApplication No. H8-290778A (Patent Document 1), a system stability andsensitivity characteristics of road surface information and disturbanceinformation are simultaneously designed by a robust stabilizationcompensating section within the control unit 100.

However, in such a conventional control device, since a reaction forcein a case of steering performed in the vicinity of a steering neutralposition is small, due to the influence of friction, it is difficult toaccurately transmit the road surface information to a driver. Further,it is difficult for the conventional electric power steering apparatusto let a hysteresis characteristic between a steering angle and thesteering force be a characteristic the same as that of a hydraulic powersteering.

As an apparatus for solving such a problem, there is an apparatusdisclosed in Japanese Published Unexamined Patent Application No.2002-369565 A (Patent Document 2).

A gross outline of the apparatus disclosed in Patent Document 2 will bedescribed with reference to FIG. 2 corresponding to FIG. 1. As shown inFIG. 2, the motor 20 for generating the steering assist torque of thesteering apparatus is driven by a motor driving section 21, the motordriving section 21 is controlled by the control unit 100 indicated by adashed-two dotted line, and the steering torque Th from the torquesensor 10 and the vehicle velocity Vel from a vehicle velocity detectingsystem are inputted into the control unit 100. In the motor 20, a motorinter-terminal voltage Vm and a motor current value i are measured andoutputted.

The control unit 100 comprises a torque system control unit 110indicated by a dashed line that performs a control by using the steeringtorque Th and a motor system control unit 120 indicated by adashed-dotted line that performs a control relating to driving of themotor 20. The torque system control unit 110 comprises an assist amountcalculating section 111, a differential control section 112, a yaw rateconvergence control section 113, a robust stabilization compensatingsection 114 and an SAT (Self Aligning Torque) estimation feedbacksection 115, addition sections 116A and 116B, and a subtraction section116C. Further, the motor system control unit 120 comprises acompensating section 121, a disturbance estimating section 122, a motorangular velocity calculating section 123, a motor angular accelerationcalculating section 124, a motor characteristic compensating section125, and addition sections 126A and 126B.

The steering torque Th is inputted into the assist amount calculatingsection 111, the differential control section 112, the yaw rateconvergence control section 113 and the SAT estimation feedback section115, and all of them input the vehicle velocity Vel as a parameter. Theassist amount calculating section 111 calculates an assist torque amountbased on the steering torque Th. The yaw rate convergence controlsection 113 inputs the steering torque Th and a motor angular velocityω, and brakes a movement that the steering wheel whirls to improve theconvergence of yaw of the vehicle. Further, the differential controlsection 112 enhances a control responsibility in the vicinity of theneutral position of the steering and realizes a smooth steering.Moreover, the SAT estimation feedback section 115 inputs the steeringtorque Th, a signal obtained in the addition section 116A by adding theoutput of the differential control section 112 to the output of theassist amount calculating section 111, the motor angular velocity ωcalculated by the motor angular velocity calculating section 123 and amotor angular acceleration α from the motor angular accelerationcalculating section 124 to estimate an SAT, performs signal processingby using a feedback filter with respect to the estimated SAT, andprovides the steering wheel with a suitable road information as areaction force.

Further, a signal that is obtained in the addition section 116B byadding the output of the yaw rate convergence control section 113 to asignal obtained in the addition section 116A by adding the output of thedifferential control section 112 to the output of the assist amountcalculating section 111, is inputted into the robust stabilizationcompensating section 114 as an assist amount AQ. For example, the robuststabilization compensating section 114 is a compensating sectiondisclosed in Japanese Published Unexamined Patent Application No.H8-290778 A, removes a peak value in a resonance frequency of aresonance system comprised of an inertia element and a spring elementthat are included in the detected torque, and compensates a phase shiftof the resonance frequency that disturbs the responsibility and thestability of the control system. By subtracting the output of the SATestimation feedback section 115 from the output of the robuststabilization compensating section 114 in the subtraction section 116C,an assist amount Ia capable of transmitting the road information to thesteering wheel as the reaction force, is obtained.

Moreover, the motor angular velocity calculating section 123 calculatesthe motor angular velocity ω based on the motor inter-terminal voltageVm and the motor current value i, and the motor angular velocity ω isinputted into the motor angular acceleration calculating section 124,the yaw rate convergence control section 113 and the SAT estimationfeedback section 115. The motor angular acceleration calculating section124 calculates the motor angular acceleration α based on the inputtedmotor angular velocity ω, and the calculated motor angular accelerationα is inputted into the motor characteristic compensating section 125. Inthe addition sections 126A, the assist amount Ia obtained by subtractingthe output of the SAT estimation feedback section 115 from the output ofthe robust stabilization compensating section 114, is added to theoutput Ic of the motor characteristic compensating section 125, and thenthis added signal is inputted into the compensating section 121comprised of a differential compensating section or the like as acurrent command value Ir. A signal that is obtained by adding the outputof the disturbance estimating section 122 in the addition section 126Bto a current command value Ira obtained by compensating the currentcommand value Ir by means of the compensating section 121, is inputtedinto the motor driving section 21 and the disturbance estimating section122. The disturbance estimating section 122 is an apparatus disclosed inJapanese Published Unexamined Patent Application No. H8-310417 A, iscapable of maintaining a desired motor control characteristic in anoutput reference of the control system based on a signal obtained byadding the output of the disturbance estimating section 122 to thecurrent command value Ira compensated by the compensating section 121that is the control target of the motor output and the motor currentvalue i, and does not lose the stability of the control system.

Here, the aspects of torques generated between a road surface and asteering will be described with reference to FIG. 3. When the driversteers the steering wheel 1, the steering torque Th is generated andthen the motor 20 generates an assist torque Tm in accordance with thesteering torque Th. As a result, wheels are steered and the SAT isgenerated as the reaction force. Further, in such case, due to aninertia J and a friction (a static friction) Fr of the motor 20, atorque becoming the resistance of steering the steering wheel, isgenerated. By considering a balance between these forces, and by settinga sign( ) as a sign function, a motion equation such as the followingExpression 1 is obtained.

J˜·+Fr˜sign(ω)+SAT=Tm+Th  [Expression 1]

Here, by setting initial values to zero, performing a Laplace transformfor the above Expression 1 and then solving with respect to the SAT, thefollowing Expression 2 is obtained.

SAT(s)=Tm(s)+Th(s)−J−α(s)−Fr−sign(ω(s))  [Expression 2]

It is clear from the above Expression 2 that by preliminarily obtainingthe inertia J and the static friction Fr of the motor 20 as constants,it is possible to estimate the SAT based on the motor angular velocityω, the motor angular acceleration α, the steering assist torque Tm andthe steering torque Th. For such a reason, the steering torque Th, themotor angular velocity ω, the motor angular acceleration α and theoutput of the assist amount calculating section 111 are inputted intothe SAT estimation feedback section 115.

Further, in the case of directly feeding back an SAT estimation currentvalue *SAT estimated by the SAT estimation feedback section 115 withoutany processing, since the steering becomes too heavy, it is impossibleto improve the steering feeling. Therefore, as shown in FIG. 4, a signalprocessing is performed with respect to the SAT estimation current value*SAT by using a feedback filter 115A having a vehicle velocity sensitivegain and a frequency characteristic, and only necessary and sufficientinformation for improving the steering feeling is fed back. The feedbackfilter 115A used in here comprises a Q-filter (phase-lag) 115B having again as a static characteristic gain that reduces the amplitude of theestimated SAT to a necessary and sufficient value and a gain section115C having a gain characteristic shown in FIG. 5 that is sensitive tothe vehicle velocity Vel, and decreases the road surface information tofeed back in the case that the importance of the road surfaceinformation such as a static steering or a low speed driving isrelatively low.

Although the apparatus described in the above Patent Document 2configures the feedback of SAT estimation so that a frequency band inwhich there are disturbances that need to be suppressed and a frequencyband in which there are disturbances that need to be transmitted arecompatible, there is no function that actively cancels out thedisturbances that need to be suppressed.

On the other hand, in the vehicle, at ordinary braking and steady-staterunning, a brake judder and a shimmy that give annoyance to passengersoccur. The brake judder is a floor and pedal vibration occurring atbraking of the vehicle, and sometimes induces a vibration in steeringrotation direction. A variation in braking torque caused by DTV (DiskThickness Variation) of the brake disk is the excitation source of thebrake judder and has the first-order and higher-order components of thewheel rotation. It is amplified by the fore-and-aft resonance of thesuspension and transmitted through the vehicle body and the steeringsystem, and ultimately becomes the floor and pedal vibration and thesteering vibration. Further, the shimmy is a vibration that occurs inthe steering rotation direction during running of the vehicle. Animbalance and non-uniformity of rotating parts such as tires and wheelsbecome the excitation source of the shimmy. It is amplified by thesuspension resonance and then becomes the vibration in steering rotationdirection through the steering system.

The apparatus of Patent Document 2 does not consider the brake judderand the shimmy described above at all. Further, in Japanese PublishedUnexamined Patent Application No. 2002-145075 A (Patent Document 3) andJapanese Published Unexamined Patent Application No. 2002-161969 A(Patent Document 4), although apparatuses that damp vibrations due tothe brake judder and the shimmy are disclosed, both of which aremechanical handling, and there is a problem that the cost increases andsimultaneously a finely-tuned suppression such as the vehicle velocitysensitive is impossible.

Furthermore, in the case that the inertia and the friction of thesteering system are large, although the vibrations due to the brakejudder do not spread to the steering wheel, for the sake of a goodsteering feeling and a vehicle stability, it is preferred that theinertia and the friction of the steering system are minimal.

In such an electric power steering apparatus, recently, vehiclesequipped with a parking support function (parking assist) that switchesan automatic steering mode and a manual steering mode appear. In avehicle equipped with the parking support function, a target steeringangle is set based on data from a camera (image), a distance sensor orthe like, and an automatic control in accordance with the targetsteering angle, is performed.

In PCT Publication No. WO2008/146372 (Patent Document 5), the steeredwheel is steered depending on driver's steering wheel operation bycomprising a target driving amount calculating section that generates atarget auxiliary steering angle or a target steered angle added by anauxiliary steering angle superposition mechanism based on asteering-wheel steering angle detection value from a steering wheelangle detecting section and a transmission characteristic, andcalculates a target driving amount of a motor so as to make the targetauxiliary steering angle and an auxiliary steering angle detection valuefrom an auxiliary steering angle detecting section coincide with eachother or so as to make the target steered angle and a steered angledetection value from a steered angle detecting section coincide witheach other, and a motor driving section that drives the motor inaccordance with the target driving amount.

THE LIST OF PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Published Unexamined Patent Application    No. H8-290778 A-   Patent Document 2: Japanese Published Unexamined Patent Application    No. 2002-369565 A-   Patent Document 3: Japanese Published Unexamined Patent Application    No. 2002-145075A-   Patent Document 4: Japanese Published Unexamined Patent Application    No. 2002-161969 A-   Patent Document 5: PCT Publication No. WO2008/146372

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the electric power steering apparatus disclosed in PatentDocument 5, since a rate limit processing is not performed with respectto the target steering angle, when the target steering angle changesrapidly, the steering feeling of the driver is impaired. Further, sincea gain control in accordance with the vehicle velocity is not performed,there is a problem that it is impossible to perform a precise controlcorresponding to the vehicle velocity.

Further, although the steering angle control of the steering wheel isperformed in the automatic steering mode such as a parking support, anautomatic running or the like, since the friction (SAT) that tiresreceive from the road surface varies due to the influences of thevehicle velocity, the road surface condition (inclination, moisture,etc.) and so on, there is a problem that the follow-up capability of theactual steering angle with respect to the target steering angle of thecolumn shaft angle varies, and solution for such a problem is alsorequired.

The present invention has been developed in view of the above-describedcircumstances, and an object of the present invention is to provide anelectric power steering apparatus that is capable of obtaining a safeand comfortable steering performance by performing a signal processingin a high frequency domain with respect to the road surface informationand so on to realize an easy tuning and achieve suppression of the brakejudder and the shimmy and accurately steering in accordance with thecalculated target steering angle in the automatic steering mode (theparking support function), simultaneously, is capable of smoothlysteering even if the target steering angle is a rapid steering andconstantly following up the target steering angle by raising theresponsibility or a steady-state deviation even in a low vehiclevelocity.

Means for Solving the Problems

The present invention relates to an electric power steering apparatusthat calculates a first motor current command value based on a steeringtorque and a vehicle velocity, performs an assist control of a steeringsystem by driving a motor based on said first motor current commandvalue, and has a function for switching between an automatic steeringmode and a manual steering mode, the above-described object of thepresent invention is achieved by that comprising: a steering anglecontrol section that calculates a second motor current command valuebased on a target steering angle, an actual steering angle, a motorangular velocity and a motor angular acceleration of said motor, saidsteering torque and a previous time current command value; and aswitching section that inputs said first motor current command value andsaid second motor current command value to switch, wherein said steeringangle control section comprises a feedback control section thatgenerates a feedback control current command value based on said targetsteering angle, said actual steering angle, said motor angular velocityand said steering angle; an SAT compensating section that generates anSAT compensation current command value based on said motor angularvelocity, said motor angular acceleration, said steering torque and saidprevious time current command value; and an output section thatgenerates said second motor current command value from said feedbackcontrol current command value and said SAT compensation current commandvalue, wherein said switching section is switched depending on aswitching command of said automatic steering mode and said manualsteering mode, said motor is drive-controlled based on said second motorcurrent command value in said automatic steering mode.

Further, the above-described object of the present invention is moreeffectively achieved by that wherein said feedback control sectioncomprises a rate limiter that performs a smoothing with respect to saidtarget steering angle; a low pass filter (LPF) that is connected to anoutput of said rate limiter; a first proportional gain section thatmultiplies an angle deviation between an output of said LPF and saidactual steering angle by a proportional gain; an integral gain sectionthat integrates a velocity deviation between an error velocity from saidfirst proportional gain section and said motor angular velocity andmultiplies said integrated velocity deviation by an integral gain; asecond proportional gain section that multiplies said velocity deviationby a proportional gain; a differential gain section that differentiatessaid steering torque and multiplies said differentiated steering torqueby a differential gain; and an output section that performs an additionthat adds an output of said differential gain section to a deviationvalue between an output of said integral gain section and an output ofsaid second proportional gain section, limits a result of said additionby an upper and a lower limit values and outputs said feedback controlcurrent command value; or wherein said SAT compensating sectioncomprises an SAT estimating section that calculates an SAT estimationcurrent value based on said steering torque, said motor angularvelocity, said motor angular acceleration and said previous time currentcommand value; a low pass filter (LPF) that inputs said SAT estimationcurrent value and simultaneously has a characteristic that a cut-offfrequency is higher than an angle response frequency; and a vehiclevelocity sensitive gain section that multiplies an output of said LPF bya vehicle velocity variable gain and outputs said SAT compensationcurrent command value; or wherein said SAT estimating section comprisesa viscous friction coefficient section that multiplies said motorangular velocity by a viscous friction coefficient; a signizationCoulomb friction section that signizes said motor angular velocity andmultiplies said signized motor angular velocity by a Coulomb friction;an overall inertial moment section that multiplies said motor angularacceleration by an overall inertial moment; and an output coefficientsection that performs a subtraction that subtracts said steering torquefrom an addition value of an output of said viscous friction coefficientsection and an output of said signization Coulomb friction section,performs an addition that adds an output of said overall inertial momentsection to a result of said subtraction, and multiplies a result of saidaddition by a coefficient; or wherein said SAT estimating sectioncomprises an addition section that adds a current command valuecorresponding to an assist torque and said steering torque; a firstsubtraction section that subtracts a value obtained by multiplying saidmotor angular acceleration by an inertial from an addition result ofsaid addition section; and a second subtraction section that subtracts avalue obtained by signizing said motor angular velocity and multiplyingsaid signized motor angular velocity by a friction from a subtractionresult of said first subtraction section, and outputs said SATestimation current value; or wherein a limiter that limits an upper anda lower limit values is connected to a post-stage of said vehiclevelocity sensitive gain section.

Effects of the Invention

According to an electric power steering apparatus of the presentinvention, in a vehicle having the automatic steering mode (parkingsupport function) and the manual steering mode, since the targetsteering angle to calculate based on data from a camera (image), adistance sensor or the like is calculated with considering the vehiclevelocity, it is possible to accurately steer with respect to the targetsteering angle, and simultaneously, the driver does not feel anuncomfortable feeling. Further, with respect to a radical targetsteering angle, since the smoothing of the rapid target steering angleis performed to control, the driver does not feel an anxious feelingeven in automatic operation.

In addition, since the electric power steering apparatus of the presentinvention raises the responsibility or the steady-state deviation byraising the control gain in the case of a low vehicle velocity, it ispossible to bring the actual steering angle close to the target steeringangle even in a low vehicle velocity.

Moreover, since the electric power steering apparatus of the presentinvention estimates an SAT, performs filtering of the estimated SAT bymeans of an LPF (Low Pass Filter) that a cut-off frequency higher thanan angle response frequency is set, multiplies a value after filteringby a vehicle velocity gain set in accordance with the vehicle velocityand adds the multiplication result as a compensation value, it ispossible to more improve the follow-up capability of the actual steeringangle to the target steering angle.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a configuration diagram illustrating a general outline of anelectric power steering apparatus;

FIG. 2 is a block diagram showing a configuration example of a controlsystem of the electric power steering apparatus;

FIG. 3 is a conceptual diagram illustrating aspects of torques generatedbetween a road surface and a steering system;

FIG. 4 is a block diagram showing a configuration example of a feedbacksection;

FIG. 5 is a diagram showing a characteristic example of a feedbackfilter;

FIGS. 6(A), (B) and (C) are characteristic diagrams for explaining theprinciple of the present invention;

FIG. 7 is a block diagram showing a configuration example of the presentinvention;

FIG. 8 is a block diagram showing a configuration example of a steeringangle control section;

FIG. 9 is a block diagram showing a configuration example of a feedbackcontrol section;

FIG. 10 is a block diagram showing a configuration example of a ratelimiter;

FIG. 11 is a block diagram showing a configuration example of avariation amount setting section;

FIG. 12 is a block diagram showing one configuration example of an SATcompensating section;

FIG. 13 is a characteristic diagram showing a characteristic example ofa vehicle velocity sensitive gain section;

FIG. 14 is a flowchart showing an operation example of the presentinvention;

FIG. 15 is a flowchart showing an operation example of the steeringangle control section;

FIG. 16 is a flowchart showing an operation example of the feedbackcontrol section;

FIG. 17 is a flowchart showing an operation example of the SATcompensating section; and

FIG. 18 is a block diagram showing another configuration example of theSAT compensating section.

MODE FOR CARRYING OUT THE INVENTION

Although the steering angle control of the steering wheel is performedin the automatic steering mode such as a parking support, an automaticrunning or the like, since the friction (SAT (Self Aligning Torque))that tires receive from the road surface varies due to the influences ofthe vehicle velocity, the road surface condition (inclination, moisture,etc.) and so on, there is a problem that the follow-up capability of theactual steering angle with respect to the target steering angle of thecolumn shaft angle varies. In order to solve this problem, the presentinvention estimates an SAT, performs filtering of the estimated SAT bymeans of an LPF (Low Pass Filter) that a cut-off frequency higher thanan angle response frequency is set, multiplies an SAT value afterfiltering by a vehicle velocity gain set in accordance with the vehiclevelocity and adds the multiplication result as a compensation value to acurrent command value so as to improve the follow-up capability of theactual steering angle to the target steering angle.

The present invention generates a motor torque in a direction cancellingout the influence of the reaction force (SAT) that tires receive fromthe road surface by adding an SAT compensation current command valuegenerated in an SAT compensating section to a feedback control currentcommand value generated in a feedback control section. In this way, itis possible to suppress the influence of SAT-disturbances occurringduring the steering angle control and improve the follow-up capabilityof the steering angle control with respect to the target steering angle.For example, as an example of the parking support operation, since theSAT varies depending on a friction p between the tires and the roadsurface, and the steering angle response also varies in accordance withthis, there is a problem that the handling of the vehicle side becomesdifficult. For another example, in the case that an inclination of theroad surface occurs in the right and left directions of the vehicle bodyduring the automatic running, since the SAT is applied to one direction,there is a problem that due to this influence, shift of the steeringangle with respect to the target steering angle occurs temporarily. As ameans of solving these problems, by subtracting the SAT compensationcurrent command value from the feedback control current command value,the present invention enables the steering angle control with a betterfollow-up capability.

FIG. 6(A) shows one example of a steering angle response waveform, andFIG. 6 (B) shows one example of an SAT estimation value waveform. FIGS.6(A) and 6(B) show each response waveform in the case that anSAT-disturbance step shown in FIG. 6(C) is inputted after 1 second froma time (second) 0. In the present invention, an LPF (Low Pass Filter)that cuts high-frequency components of the disturbance is used in acompensation path of the SAT estimation value that has a function ofextracting the disturbance components to cancel out, and the steeringangle response waveform and the SAT estimation value waveform varydepending on the magnitude of LPF's cut-off frequency Fc. When theSAT-disturbance step shown in FIG. 6(C) is inputted, with respect to theSAT estimation value waveform shown in FIG. 6 (B), as indicated by anarrow B, its rising becomes large as the LPF's cut-off frequency Fcbecomes large, and it is possible to cancel out the disturbance at ahigh speed. In this way, as shown in FIG. 6 (A), the steering anglevaries from “absence of SAT estimation” like an arrow A, it is possibleto improve the steering angle responsibility as the LPF's cut-offfrequency Fc is increased. Consequently, it is possible to suppress thesudden rotation of the steering wheel.

Further, the road surface reaction force (SAT) transmitted to thesteering system through the tires, is different depending on the vehiclevelocity even in the case of the vehicle having the automatic steeringmode and the manual steering mode. Therefore, in the automatic steeringmode, when the automatic control of the steering is performed based onthe calculated target steering angle, the steering angle response isdifferent depending on the vehicle velocity. Thus, the present inventionadjusts a motor current command value for the automatic controldepending on the vehicle velocity to reduce the influence of the roadsurface reaction force that tires receive from the road surface.Furthermore, since the present invention performs a smoothing processingby a rate limiter with respect to the target steering angle, an effectthat moderates the response of the steering angle of the steering wheeleven when the target steering angle has an abrupt change can beachieved. It is possible to accurately move the vehicle with respect tothe target steering angle regardless of the vehicle velocity, and it issafer for the driver.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 7 is a block diagram showing a configuration example of the presentinvention. As shown in FIG. 7, a rotation angle sensor 151 for detectinga motor rotation angle θs such as a resolver is connected to a motor150, and the motor 150 is drive-controlled via a vehicle side ECU 130and an EPS (Electric Power Steering apparatus) side ECU 140.

The vehicle side ECU 130 comprises a switching command section 131 thatoutputs a switching command SW of the automatic steering mode or themanual steering mode based on a button, a switch or the like indicatingthe intention of a driver and a target steering angle generating section132 that generates a target steering angle θt based on a signal from acamera (image), a distance sensor or the like. Further, an actualsteering angle θr detected by a steering angle sensor 152 provided onthe column shaft and a vehicle velocity Vel from a vehicle velocitysensor 153, are inputted into a steering angle control section 200within the EPS side ECU 140 through the vehicle side ECU 130. Thesteering angle sensor 152 may be a steering angle estimation value basedon the column shaft (including an intermediate shaft, a pinion shaft),the displacement of rack of the rack and pinion or a wheel velocity.Further, it is also possible to receive the vehicle velocity Vel fromthe CAN or the like.

The switching command section 131 outputs the switching command SW basedon a signal that identifies entering the automatic steering mode, forexample, based on the button or the switch indicating the intention ofthe driver that is provided on a dashboard or on the periphery of thesteering wheel, or a vehicle state signal represented by a parking modeor the like provided on the shift, and then the switching command SW isinputted into a switching section 142 within the EPS side ECU 140.Further, the target steering angle generating section 132 generates thetarget steering angle θt based on data from the camera (image), thedistance sensor or the like by means of a publicly-known method, andinputs the generated target steering angle θt into the steering anglecontrol section 200 within the EPS side ECU 140.

The EPS side ECU 140 comprises a torque control section 141 that outputsa motor current command value Itref calculated as previously describedbased on the steering torque Th and the vehicle velocity Vel, thesteering angle control section 200 that calculates a motor currentcommand value Imref for the steering angle automatic control based onthe target steering angle θt, the actual steering angle θr, the vehiclevelocity Vel, the steering torque Th from a torque sensor 154, the motorangular velocity co and a motor angular acceleration α and outputs thecalculated motor current command value Imref, the switching section 142that switches between the motor current command values Itref and Imrefdepending on the switching command SW, a current control/drive section143 that drive-controls the motor 150 based on the motor current commandvalue (Itref or Imref) from the switching section 142, a motor angularvelocity calculating section 144 that calculates the motor angularvelocity ω based on the motor rotation angle θs from the rotation anglesensor 151 and a motor angular acceleration calculating section 145 thatcalculates the motor angular acceleration α based on the motor angularvelocity ω. The switching section 142 switches between a torque controlmode (the manual steering mode) by the torque control section 141 andthe automatic steering mode by the steering angle control section 200based on the switching command SW from the switching command section 131within the vehicle side ECU 130, in the torque control mode, outputs themotor current command value Itref, and in the automatic steering mode,outputs the motor current command value Imref. Further, the currentcontrol/drive section 143 comprises a PI current control section, a PWMcontrol section, an inverter and so on.

The steering angle control section 200 has a configuration shown in FIG.8. As shown in FIG. 8, the steering angle control section 200 comprisesa feedback control section 210 that inputs the target steering angle θt,the actual steering angle θr, the motor angular velocity ω and thesteering torque Th and calculates a feedback control current commandvalue Ifref to output, an SAT compensating section 230 that inputs themotor angular velocity co, the steering torque Th, the motor angularacceleration α and a previous time current command value Iref (Z⁻¹) andcalculates an SAT compensation current command value Isref to output, anaddition section 201 that adds the SAT compensation current commandvalue Isref to the feedback control current command value Ifref andoutputs a motor current command value Imo, and an addition section 202that adds a current command value to the motor current command value Imoand outputs a motor current command value Imref.

The feedback control section 210 has a function that suppresses atorsional vibration caused by a torsion bar and a steering inertia.Further, an output section is comprised of the addition section 201 andthe addition section 202.

The feedback control section 210 has a configuration shown in FIG. 9 andis a position control system that sets a velocity control loop system asa minor loop. As shown in FIG. 9, the target steering angle θt isinputted into a rate limiter 211 that performs a smoothing when thetarget steering angle θt changes rapidly, that is, makes the targetsteering angle θt change smoothly within the range of a predeterminedtime change rate, and a target steering angle θta passed through an LPF212 for removing high-frequency disturbances is addition-inputted into asubtraction section 213A. The actual steering angle θr issubtraction-inputted into the subtraction section 213A, an angledeviation between the actual steering angle θr and the smoothed targetsteering angle θta, is multiplied by a gain Kpp in a proportional gain(Kpp) section 214 and then addition-inputted into a subtraction section213B as an error velocity ωe. The motor angular velocity ω from themotor angular velocity calculating section 144 is subtraction-inputtedinto the subtraction section 213B, the calculated velocity deviation Dfis multiplied by gain Kvi in an integral gain (Kvi) section 216B via anintegral section 216A and then addition-inputted into a subtractionsection 213C, simultaneously, the velocity deviation Df is multiplied bygain Kvp in a proportional gain (Kvp) section 216C and thensubtraction-inputted into the subtraction section 213C. The subtractionresult of the subtraction section 213C is inputted into an additionsection 213D.

The steering torque Th from the torque sensor 154 is multiplied by again Kc in a differential gain (Kc) section 215B via a differentialsection 215A and then inputted into an addition section 213D, theaddition result of the addition section 213D is limited by an upper anda lower limit values in a limiter 217 and outputted as the feedbackcontrol current command value Ifref. An output section is comprised ofthe subtraction section 213C, the addition section 213D and the limiter217.

The rate limiter 211 performs a smoothing with respect to the targetsteering angle θt and outputs the smoothed target steering angle θt whenthe target steering angle θt changes rapidly, for example, has aconfiguration shown in FIG. 10. As shown in FIG. 10, the target steeringangle θt is addition-inputted into a subtraction section 211-1,depending on a steering angle θt1 being the subtraction result obtainedby subtracting a past value from the target steering angle θt, avariation-amount setting section 211-2 sets a variation amount θt2. Thevariation-amount setting section 211-2 sets a difference θt1 between thepast value from a holding section (Z⁻¹) 211-4 and the input (θt), andthe addition result obtained by adding the past value to thevariation-amount θt2 in an addition section 211-3 is outputted as a newtarget steering angle θt3. The variation-amount setting section 211-2makes the variation-amount not exceeding an upper limit and a lowerlimit that are set, that characteristic obtains the difference with theinput (target steering angle) et at each of calculation periods, in thecase of falling outside the upper limit and the lower limit of thevariation-amount setting section 211-2, by repeatedly performing addingthe difference to the past value, the output θt3 varies in a staircasepattern shown in FIG. 11 and finally matching the output θt3 with thetarget steering angle θt. Further, in the case that the difference withthe input (target steering angle) et is within the range of the upperlimit and the lower limit of the variation-amount setting section 211-2,since the variation-amount θt2 (=the difference θt1) is outputted andadded to the past value, the result output θt3 coincides with the input(target steering angle) et. As these results, even if the targetsteering angle θt changes rapidly, it is possible to smoothly vary thetarget steering angle θt changing rapidly, a sudden current variation(i.e. a steering at a high speed) is prevented, a function that reducesan anxious feeling relating to the automatic operation of the driver isfulfilled.

The SAT compensating section 230 obtains an SAT torque (column shaftconversion) from a motion equation around the column shaft and obtainsan SAT estimation current value I_(SAT) being a motor current thatcorresponds to the SAT torque. Then, the SAT estimation current valueI_(SAT) is passed through the LPF that the cut-off frequency higher thanthe angle response frequency is set, further multiplied by a vehiclevelocity sensitive gain set by the vehicle velocity, and obtains the SATcompensation current command value Isref.

In obtaining the SAT torque (column shaft conversion) from the motionequation around the column shaft and obtaining the SAT estimationcurrent value I_(SAT) corresponding to the SAT torque, the followingExpression 3 is used.

$\begin{matrix}{\mspace{20mu} {{{I_{c}{\overset{.}{\omega}}_{c}} = {T_{sat} + {K_{t}i} + T_{h} - {c\; \omega_{c}} - {T_{Frc} \cdot {{sign}\left( \omega_{c} \right)}}}}\mspace{20mu} {T_{sat} = {{I_{c}{\overset{.}{\omega}}_{c}} - {K_{t}i} - T_{h} + {c\; \omega_{c}} + {T_{Frc} \cdot {{sign}\left( \omega_{c} \right)}}}}{I_{sat} = {\frac{T_{sat}}{K_{t}} = {{- i} + {\frac{1}{K_{t}}\left( {{- T_{h}} + {I_{c}{\overset{.}{\omega}}_{c}} + {c\; \omega_{c}} + {T_{Frc} \cdot {{sign}\left( \omega_{c} \right)}}} \right)}}}}}} & \left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack\end{matrix}$

-   -   Where Ic is an overall inertial moment of a column converted to        the column shaft, the rack and pinion mechanism and the tires,        ω_(c) is a column shaft angular velocity, Th is the steering        torque (a torsion torque of a torsion bar), T_(Frc) is a Coulomb        friction acting on the column shaft, c is a column shaft viscous        friction coefficient, and Kt is a coefficient (a motor torque        constant×a reduction ratio) that converts from the current value        to the torque of the column shaft.

The SAT compensating section 230 based on the above Expression 3 has aconfiguration shown in FIG. 12. As shown in FIG. 12, the motor angularvelocity ω is inputted into a viscous friction coefficient (c) section231, multiplied by the viscous friction coefficient c andaddition-inputted into an addition and subtraction section 232A,simultaneously, is signized by a sign section 233, multiplied by theCoulomb friction I_(Frc) in a Coulomb friction (T_(Frc)) section 234 andaddition-inputted into the addition and subtraction section 232A. Asignization Coulomb friction section is comprised of the sign section233 and the Coulomb friction section 234. Further, the steering torqueTh is subtraction-inputted into the addition and subtraction section232A, and the addition and subtraction result is addition-inputted intoan addition section 232B. The motor angular acceleration α (here, themotor angular acceleration α is considered as being equal to a columnshaft angular acceleration) is inputted into an overall inertial moment(Ic) section 235, multiplied by the overall inertial moment Ic andinputted into the addition section 232B. The addition result obtained inthe addition section 232B is inputted into a coefficient (1/Kt) section236, multiplied by 1/Kt and addition-inputted into a subtraction section232C. The previous time current command value Iref(Z⁻¹) issubtraction-inputted into the subtraction section 232C, and thedifference is outputted as the SAT estimation current value I_(SAT) thatgenerates the motor torque corresponding to the SAT. An outputcoefficient section is comprised of the addition section 232B, thecoefficient section 236 and the subtraction section 232C.

When adding the SAT estimation current value I_(SAT) to the currentcommand value without any change, since vibrations and noises are easyto occur, filtering of the SAT estimation current value I_(SAT) isperformed by an LPF 237 having a characteristic that the cut-offfrequency is higher than a response frequency (for example, 1 Hz) of thesteering angle control. An output of the filtering of the LPF 237 ismultiplied by a gain G in a gain (G) section 238. The current commandvalue multiplied by the gain G is limited by an upper and a lower limitvalues in a limiter 239, and the SAT compensation current command valueIsref is outputted from the limiter 239. The limiter 239 is not alwaysrequired. The gain section 238 may be sensitive to the vehicle velocity,and a gain G characteristic of a vehicle velocity sensitive gain may bea characteristic that for example, as shown in FIG. 13, the gain Ggradually becomes small according to an increase in the vehicle velocityVel.

In such a configuration, an entire operation example of the presentinvention will be described with reference to a flowchart shown in FIG.14.

When the operation of the steering system starts, the torque control bythe torque control section 141 is carried out (Step S1), and the motor150 is driven by using the motor current command value Itref and bymeans of the current control/drive section 143 (Step S2). The aboveoperations are repeatedly performed until the switching command SW isoutputted from the switching command section 131 (Step S3).

When becoming the automatic steering mode and the switching command SWis outputted from the switching command section 131, the target steeringangle θt is inputted from the target steering angle generating section132 (Step S4), the actual steering angle θr is inputted from thesteering angle sensor 152 (Step S5), the steering torque Th is inputtedfrom the torque sensor 154 (Step S6), the vehicle velocity Vel isinputted from the vehicle velocity sensor 153 (Step S7), the motorangular velocity ω is inputted from the motor angular velocitycalculating section 144 (Step S8), further the motor angularacceleration α is inputted from the motor angular accelerationcalculating section 145 (Step S9), and then the motor current commandvalue Imref is generated by the steering angle control section 200 (StepS100). Moreover, the target steering angle θt, the actual steering angleθr, the steering torque Th, the motor angular velocity ω and the motorangular acceleration α can be inputted in an arbitrary order.

Then, the switching section 142 is switched by the switching command SWfrom the switching command section 131 (Step S10), the motor 150 isdriven by using the motor current command value Imref from the steeringangle control section 200 and by means of the current control/drivesection 143 (Step S11), and a return to the above Step S3 is made. Thedrive control based on the motor current command value Imref isrepeatedly performed until the switching command SW is changed from theswitching command section 131.

The generation of the motor current command value Imref is performed bythe steering angle control section 200, and a flowchart of FIG. 15 showsthe generating operation of the motor current command value Imrefperformed in the steering angle control section 200.

Firstly, the feedback control section 210 inputs the target steeringangle θt, the actual steering angle θr, the motor angular velocity ω andthe steering torque Th (Step S101), and generates the feedback controlcurrent command value Ifref (Step S102). Concurrently, the SATcompensating section 230 inputs the motor angular velocity ω, thesteering torque Th, the motor angular acceleration α and the previoustime current command value Iref (Z⁻¹) (Step S103), and generates the SATcompensation current command value Isref (Step S104). The feedbackcontrol current command value Ifref is inputted into the additionsection 201, and simultaneously the SAT compensation current commandvalue Isref is inputted into the addition section 201 (Step S105). Theaddition section 202 adds the current command value to the currentcommand value Imo (=Ifref−Imref) being the addition result obtained inthe addition section 201 and outputs the motor current command valueImref.

Next, operations of the feedback control section 210 will be describedwith reference to a flowchart shown in FIG. 16.

The target steering angle θt is inputted into the rate limiter 211 (StepS110), the rate limiting operation described as above is performed inthe rate limiter 211 (Step S111), and the target steering angle θta thatpassed through the LPF 212 is inputted into the subtraction section213A. Further, the actual steering angle θr is inputted from thesteering angle sensor 152 (Step S112), the subtraction of “θta−θr” isperformed in the subtraction section 213A (Step S113), the angledeviation θd being the subtraction result obtained in the subtractionsection 213A is multiplied by the gain Kpp in the proportional gainsection 214 and addition-inputted into the subtraction section 213B(Step S114). The motor angular velocity ω is subtraction-inputted intothe subtraction section 213B, and the velocity deviation between themotor angular velocity ω and the angular velocity multiplied by the gainKpp is obtained (Step S115). The velocity deviation obtained in thesubtraction section 213B is integrated by the integral section 216A,multiplied by the gain Kvi in the integral gain section 216B andaddition-inputted into the subtraction section 213C (Step S116),simultaneously, is multiplied by the proportional gain Kvp in theproportional gain section 216C, subtraction-inputted into thesubtraction section 213C (Step S117) and subtracted in the subtractionsection 213C (Step S118).

Thereafter, the steering torque Th is inputted (Step S120), the steeringtorque Th is differentiated by the differential section 215A, multipliedby the differential gain Kc in the differential gain section 215B andinputted into the addition section 213D (Step S121). An output of thedifferential gain section 215B that is inputted into the additionsection 213D, is added to the subtraction result obtained in thesubtraction section 213C by means of the addition section 213D (StepS122), limited by the upper and the lower limit values in the limiter217 (Step S123), and outputted as the feedback control current commandvalue Ifref (Step S124).

Next, operations of the SAT compensating section 230 will be describedwith reference to a flowchart shown in FIG. 17.

The motor angular velocity ω and the steering torque Th are inputted(Step S130), the motor angular velocity ω is multiplied by the viscousfriction coefficient c in the viscous friction coefficient section 231(Step S131), the motor angular velocity co is signized by the signsection 233 and multiplied by the Coulomb friction I_(Frc) in theCoulomb friction section 234 (Step S132), an output of the viscousfriction coefficient section 231 and an output of the Coulomb frictionsection 234 are added, and simultaneously, the addition and subtractionsection 232A performs addition and subtraction of the steering torque Th(Step S133).

Next, the motor angular acceleration α is inputted into the overallinertial moment section 235, multiplied by the overall inertial momentIc (Step S134), and added in the addition section 232B (Step S135). Theaddition result obtained in the addition section 232B is multiplied by1/Kt in the coefficient section 236 and addition-inputted into thesubtraction section 232C, and the subtraction section 232C subtracts theprevious time current command value Iref (Z⁻¹) that is separatelyinputted (stored) from an output of the coefficient section 236 that isinputted into the subtraction section 232C (Step S137). The subtractionresult of the subtraction section 232C is outputted as the SATestimation current value I_(SAT) that generates the motor torquecorresponding to the SAT, and the filtering of the SAT estimationcurrent value I_(SAT) is performed by the LPF 237 (Step S140), thevehicle velocity Vel is inputted into the gain section 238 andmultiplied by the gain G (Step S141), further limited by the upper andthe lower limit values in the limiter 239 (Step S122), and the SATcompensation current command value Isref is outputted from the limiter239 (step S143).

Although the SAT compensating section 230 shown in FIG. 12 is configuredbased on the above Expression 3, also with respect to the SAT estimationdescribed in FIG. 4, it is possible to configure in the same way. FIG.18 shows that configuration example and it is possible to obtain the SATcompensation current command value Isref by using of the SAT estimationcurrent value *SAT (=I_(SAT)), an LPF 230-1 having a characteristic thesame as described above, a vehicle velocity sensitive type gain (G)section 230-2 and a limiter 230-3.

EXPLANATION OF REFERENCE NUMERALS

-   1 steering wheel-   2 column shaft (steering shaft)-   10,154 torque sensor-   12,153 vehicle velocity sensor-   13 battery-   20,150 motor-   21 motor driving section-   100 control unit (ECU)-   110 torque system control unit-   120 motor system control unit-   151 rotation angle sensor-   152 steering angle sensor-   130 vehicle side ECU-   131 switching command section-   132 target steering angle generating section-   140 EPS side ECU-   141 torque control section-   142 switching section-   143 current control/drive section-   144 motor angular velocity calculating section-   145 motor angular acceleration calculating section-   200 steering angle control section-   210 feedback control section-   211 rate limiter-   211-2 variation amount setting section-   211-4 holding section-   212,230-1,237 LPF (low pass filter)-   214 proportional gain section-   215A differential section-   215B differential gain (Kc) section-   216A integral section-   216B integral gain (Kvi) section-   216C proportional gain (Kvp) section-   217,239,230-3 limiter-   230 SAT compensating section-   231 viscous friction coefficient section-   233 sign section-   234 Coulomb friction section-   238 (vehicle velocity sensitive) gain section

1-9. (canceled)
 10. An electric power steering apparatus that calculatesa first motor current command value based on a steering torque and avehicle velocity, performs an assist control of a steering system bydriving a motor based on said first motor current command value, and hasa function for switching between an automatic steering mode and a manualsteering mode, comprising: a steering angle control section thatcalculates a second motor current command value based on a targetsteering angle, an actual steering angle, a motor angular velocity and amotor angular acceleration of said motor, said steering torque and aprevious time current command value; and a switching section that inputssaid first motor current command value and said second motor currentcommand value to switch, wherein said steering angle control sectioncomprises a feedback control section that generates a feedback controlcurrent command value based on said target steering angle, said actualsteering angle, said motor angular velocity and said steering angle; anSAT compensating section that generates an SAT compensation currentcommand value based on said motor angular velocity, said motor angularacceleration, said steering torque and said previous time currentcommand value; and an output section that generates said second motorcurrent command value from said feedback control current command valueand said SAT compensation current command value, wherein said feedbackcontrol section comprises a rate limiter that performs a smoothing withrespect to said target steering angle; a low pass filter (LPF) that isconnected to an output of said rate limiter; a first proportional gainsection that multiplies an angle deviation between an output of said LPFand said actual steering angle by a proportional gain; an integral gainsection that integrates a velocity deviation between an error velocityfrom said first proportional gain section and said motor angularvelocity and multiplies said integrated velocity deviation by anintegral gain; a second proportional gain section that multiplies saidvelocity deviation by a proportional gain; a differential gain sectionthat differentiates said steering torque and multiplies saiddifferentiated steering torque by a differential gain; and an outputsection that performs an addition that adds an output of saiddifferential gain section to a deviation value between an output of saidintegral gain section and an output of said second proportional gainsection, limits a result of said addition by an upper and a lower limitvalues and outputs said feedback control current command value, whereinsaid switching section is switched depending on a switching command ofsaid automatic steering mode and said manual steering mode, said motoris drive-controlled based on said second motor current command value insaid automatic steering mode.
 11. The electric power steering apparatusaccording to claim 10, wherein said SAT compensating section comprisesan SAT estimating section that calculates an SAT estimation currentvalue based on said steering torque, said motor angular velocity, saidmotor angular acceleration and said previous time current command value;a low pass filter (LPF) that inputs said SAT estimation current valueand simultaneously has a characteristic that a cut-off frequency ishigher than an angle response frequency; and a vehicle velocitysensitive gain section that multiplies an output of said LPF by avehicle velocity variable gain and outputs said SAT compensation currentcommand value.
 12. The electric power steering apparatus according toclaim 11, wherein said SAT estimating section comprises a viscousfriction coefficient section that multiplies said motor angular velocityby a viscous friction coefficient; a signization Coulomb frictionsection that signizes said motor angular velocity and multiplies saidsignized motor angular velocity by a Coulomb friction; an overallinertial moment section that multiplies said motor angular accelerationby an overall inertial moment; and an output coefficient section thatperforms a subtraction that subtracts said steering torque from anaddition value of an output of said viscous friction coefficient sectionand an output of said signization Coulomb friction section, performs anaddition that adds an output of said overall inertial moment section toa result of said subtraction, and multiplies a result of said additionby a coefficient.
 13. The electric power steering apparatus according toclaim 11, wherein a limiter that limits an upper and a lower limitvalues is connected to a post-stage of said vehicle velocity sensitivegain section.
 14. The electric power steering apparatus according toclaim 12, wherein a limiter that limits an upper and a lower limitvalues is connected to a post-stage of said vehicle velocity sensitivegain section.
 15. The electric power steering apparatus according toclaim 11, wherein said SAT estimating section comprises an additionsection that adds a current command value corresponding to an assisttorque and said steering torque; a first subtraction section thatsubtracts a value obtained by multiplying said motor angularacceleration by an inertial from an addition result of said additionsection; and a second subtraction section that subtracts a valueobtained by signizing said motor angular velocity and multiplying saidsignized motor angular velocity by a friction from a subtraction resultof said first subtraction section, and outputs said SAT estimationcurrent value.
 16. The electric power steering apparatus according toclaim 15, wherein a limiter that limits an upper and a lower limitvalues is connected to a post-stage of said vehicle velocity sensitivegain section.
 17. An electric power steering apparatus that calculates afirst motor current command value based on a steering torque and avehicle velocity, performs an assist control of a steering system bydriving a motor based on said first motor current command value, and hasa function for switching between an automatic steering mode and a manualsteering mode, comprising: a steering angle control section thatcalculates a second motor current command value based on a targetsteering angle, an actual steering angle, a motor angular velocity and amotor angular acceleration of said motor, said steering torque and aprevious time current command value; and a switching section that inputssaid first motor current command value and said second motor currentcommand value to switch, wherein said steering angle control sectioncomprises a feedback control section that generates a feedback controlcurrent command value based on said target steering angle, said actualsteering angle, said motor angular velocity and said steering angle; anSAT compensating section that generates an SAT compensation currentcommand value based on said motor angular velocity, said motor angularacceleration, said steering torque and said previous time currentcommand value; and an output section that generates said second motorcurrent command value from said feedback control current command valueand said SAT compensation current command value, wherein said SATcompensating section comprises an SAT estimating section that calculatesan SAT estimation current value based on said steering torque, saidmotor angular velocity, said motor angular acceleration and saidprevious time current command value; a low pass filter (LPF) that inputssaid SAT estimation current value and simultaneously has acharacteristic that a cut-off frequency is higher than an angle responsefrequency; and a vehicle velocity sensitive gain section that multipliesan output of said LPF by a vehicle velocity variable gain and outputssaid SAT compensation current command value, wherein said SAT estimatingsection comprises a viscous friction coefficient section that multipliessaid motor angular velocity by a viscous friction coefficient; asignization Coulomb friction section that signizes said motor angularvelocity and multiplies said signized motor angular velocity by aCoulomb friction; an overall inertial moment section that multipliessaid motor angular acceleration by an overall inertial moment; and anoutput coefficient section that performs a subtraction that subtractssaid steering torque from an addition value of an output of said viscousfriction coefficient section and an output of said signization Coulombfriction section, performs an addition that adds an output of saidoverall inertial moment section to a result of said subtraction, andmultiplies a result of said addition by a coefficient, wherein saidswitching section is switched depending on a switching command of saidautomatic steering mode and said manual steering mode, said motor isdrive-controlled based on said second motor current command value insaid automatic steering mode.
 18. The electric power steering apparatusaccording to claim 17, wherein a limiter that limits an upper and alower limit values is connected to a post-stage of said vehicle velocitysensitive gain section.